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Mitchell, Edward
Nom
Mitchell, Edward
Affiliation principale
Fonction
Professeur ordinaire
Email
edward.mitchell@unine.ch
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Résultat de la recherche
7 Résultats
Voici les éléments 1 - 7 sur 7
- PublicationAccès libreAssessing the responses of Sphagnum micro-eukaryotes to climate changes using high throughput sequencing(2020-9-18)
; ;Seppey, Christophe Victor William; ;Jassey, Vincent E.J. ;Buttler, Alexandre ;Slowinska, Sandra ;Slowinski, Michal; ;Lamentowicz, MariuszCurrent projections suggest that climate warming will be accompanied by more frequent and severe drought events. Peatlands store ca. one third of the world’s soil organic carbon. Warming and drought may cause peatlands to become carbon sources through stimulation of microbial activity increasing ecosystem respiration, with positive feedback effect on global warming. Micro-eukaryotes play a key role in the carbon cycle through food web interactions and therefore, alterations in their community structure and diversity may affect ecosystem functioning and could reflect these changes. We assessed the diversity and community composition of Sphagnum-associated eukaryotic microorganisms inhabiting peatlands and their response to experimental drought and warming using high throughput sequencing of environmental DNA. Under drier conditions, micro-eukaryotic diversity decreased, the relative abundance of autotrophs increased and that of osmotrophs (including Fungi and Peronosporomycetes) decreased. Furthermore, we identified climate change indicators that could be used as early indicators of change in peatland microbial communities and ecosystem functioning. The changes we observed indicate a shift towards a more “terrestrial” community in response to drought, in line with observed changes in the functioning of the ecosystem. - PublicationAccès librePatterns of earthworm, enchytraeid and nematode diversity and community structure in urban soils of different ages(2016-1-9)
; ;Dozsa-Farkas, Klara ;Boros, Gergely ;Rochat, Guy ;Sandoz, Gauthier; ; Annelids (Lumbricidae and Enchytraeidae) and nematodes are common soil organisms and play important roles in organic matter decomposition, nutrient cycling and creation of soil structure and porosity. However, these three groups have rarely been studied together and only few studies exist for urban soils. We studied the diversity and community composition of annelids and nematodes in soils spanning more than two centuries of urban soil development in Neuch^atel (Switzerland) and assessed the relationships 1) among these three groups and 2) between each group and environmental (physical, chemical and functional) characteristics of soils and soil age. While the groups of environmental variables were correlated (Mantel tests) no correlation was found between pairs of soil fauna groups and between each soil fauna group and environmental variables. More specifically, redundancy analyses showed that earthworm assemblages were best correlated with soil bulk density and with soil depth, the latter being positively correlated with soil age. Enchytraeid assemblages and the proportion of enchytraeid r-strategists were respectively best correlated with soil carbonate content and negatively correlated with soil age. Nematodes assemblages were best correlated with soil water content. Moreover, relationships between pairs of soil biota groups, and between each group and environmental (physical, chemical and functional) variables, varied along the soil age gradient (moving window analysis). This study provides new knowledge on urban soil biodiversity and how environmental conditions can influence soil diversity and community patterns in the urban context. The contrasted community patterns of earthworms, enchytraeids and nematodes in urban soils of different ages and their different ecological roles suggest that they represent potential complementary indicators of soil quality and functioning such as soil formation and organic matter dynamics. - PublicationAccès libreRediscovery of Nebela ansata (Amoebozoa: Arcellinida) in eastern North America: biogeographical implications(2011)
;Heger, Thierry J. ;Booth, Robert K. ;Sullivan, Maura E. ;Wilkinson, David M. ;Warner, Barry G. ;Asada, Taro ;Mazei, Yuri ;Meisterfeld, RalfAim The question whether free-living protists are generally cosmopolitan is currently a matter of debate. In this study we investigate the geographical distribution of a distinctive testate amoeba species, Nebela ansata, and use our data to assess the potential for highly restricted distribution patterns in some protist species.
Location Global.
Methods We analysed (1) 3400 testate amoeba publications from North America and other continents, (2) unpublished slides of the Penard Collection of the Natural History Museum, London, UK, and (3) 104 Sphagnum samples from eastern North America. Non-metric multidimensional scaling (NMDS) was used to visualize the similarities in testate amoeba community composition among 1012 North American samples, including two communities that contained N. ansata.
Results We rediscovered N. ansata at a site in New Jersey located close to its type locality, and in Nova Scotia. We also report the existence of an apparently unpublished museum specimen originally collected from New Jersey. Our extensive literature survey confirmed the presence of this species only in the temperate part of eastern North America. The NMDS revealed that communities with N. ansata were less similar to each other than to communities from other parts of North America, suggesting that favourable habitats for N. ansata occur in other Sphagnum-dominated peatlands, a habitat type that has been extensively sampled in North America and elsewhere.
Main conclusions These data provide an unusually convincing case of a free-living microorganism with a very limited distribution range in the temperate part of eastern North America. The remarkably restricted distribution of N. ansata highlights the extent of our ignorance about the natural history of free-living microorganisms, and raises questions about the lack of attention to microbial diversity in conservation biology. - PublicationAccès librePatterns of earthworm, enchytraeid and nematode diversity and community structure in urban soils of different ages
; ;Dózsa-Farkas, Klára ;Boros, Gergely ;Rochat, Guy ;Sandoz, Gauthier; ; Annelids (Lumbricidae and Enchytraeidae) and nematodes are common soil organisms and play important roles in organic matter decomposition, nutrient cycling and creation of soil structure and porosity. However, these three groups have rarely been studied together and only few studies exist for urban soils. We studied the diversity and community composition of annelids and nematodes in soils spanning more than two centuries of urban soil development in Neuchâtel (Switzerland) and assessed the relationships 1) among these three groups and 2) between each group and environmental (physical, chemical and functional) characteristics of soils and soil age.
While the groups of environmental variables were correlated (Mantel tests) no correlation was found between pairs of soil fauna groups and between each soil fauna group and environmental variables. More specifically, redundancy analyses showed that earthworm assemblages were best correlated with soil bulk density and with soil depth, the latter being positively correlated with soil age. Enchytraeid assemblages and the proportion of enchytraeid r-strategists were respectively best correlated with soil carbonate content and negatively correlated with soil age. Nematodes assemblages were best correlated with soil water content. Moreover, relationships between pairs of soil biota groups, and between each group and environmental (physical, chemical and functional) variables, varied along the soil age gradient (moving window analysis).
This study provides new knowledge on urban soil biodiversity and how environmental conditions can influence soil diversity and community patterns in the urban context. The contrasted community patterns of earthworms, enchytraeids and nematodes in urban soils of different ages and their different ecological roles suggest that they represent potential complementary indicators of soil quality and functioning such as soil formation and organic matter dynamics. - PublicationAccès libreAdditive partitioning of testate amoeba species diversity across habitat hierarchy within the pristine southern taiga landscape (Pechora-Ilych Biosphere Reserve, Russia)
;Tsyganov, Andrey N ;Komarov, Alexander A; ;Shimano, Satoshi ;Smirnova, Olga V ;Aleynikov, Alexey AMazei Yuri AIn order to better understand the distribution patterns of terrestrial eukaryotic microbes and the factors governing them, we studied the diversity partitioning of soil testate amoebae across levels of spatially nested habitat hierarchy in the largest European old-growth dark coniferous forest (Pechora-Ilych Biosphere Reserve; Komi Republic, Russia). The variation in testate amoeba species richness and assemblage structure was analysed in 87 samples from six biotopes in six vegetation types using an additive partitioning procedure and principal component analyses. The 80 taxa recorded represent the highest value of species richness for soil testate amoebae reported for taiga soils so far. Our results indicate that testate amoeba assemblages were highly aggregated at all levels and were mostly controlled by environmental factors rather than dispersal processes. The variation in species diversity of testate amoebae increased from the lowest to the highest hierarchical level. We conclude that, similarly to macroscopic organisms, testate amoeba species richness and community structure are primarily controlled by environmental conditions within the landscape and suggest that metacommunity dynamics of free-living microorganisms are driven by species sorting and/or mass effect processes. - PublicationAccès libreSoil protistology rebooted: 30 fundamental questions to start with
;Geisen, Stefan; ;Wilkinson, David M ;Adl, Sina ;Bonkowski, Michael ;Brown, Matthew W ;Fiore-Donno, Anna Maria; ;Jassey, Vincent E.J ;Krashevska, Valentyna ;Lahr, Daniel J.G ;Marcisz, Katarzyna; ;Payne, Richard; ;Anderson, Roger O ;Charman, Dan J ;Ekelund, Flemming ;Griffiths, Bryan S ;Rønn, Regin ;Smirnov, Alexey ;Bass, David; ;Berney, Cédric; ;Blandenier, Quentin ;Chatzinotas, Antonis ;Clarholm, Marianne ;Dunthorn, Micah ;Feest, Alan ;Fernández, Leonardo D ;Foissner, Wilhelm; ;Gentekaki, Eleni ;Hájek, Michal ;Helder, Johannes ;Jousset, Alexandre ;Koller, Robert ;Kumar, Santosh ;La Terza, Antonietta ;Lamentowicz, Mariusz ;Mazei, Yuri ;Santos, Susana S ;Seppey, Christophe V.W ;Spiegel, Frederick W ;Walochnik, Julia ;Winding, AnneProtists are the most diverse eukaryotes. These microbes are keystone organisms of soil ecosystems and regulate essential processes of soil fertility such as nutrient cycling and plant growth. Despite this, protists have received little scientific attention, especially compared to bacteria, fungi and nematodes in soil studies. Recent methodological advances, particularly in molecular biology techniques, have made the study of soil protists more accessible, and have created a resurgence of interest in soil protistology. This ongoing revolution now enables comprehensive investigations of the structure and functioning of soil protist communities, paving the way to a new era in soil biology. Instead of providing an exhaustive review, we provide a synthesis of research gaps that should be prioritized in future studies of soil protistology to guide this rapidly developing research area. Based on a synthesis of expert opinion we propose 30 key questions covering a broad range of topics including evolution, phylogenetics, functional ecology, macroecology, paleoecology, and methodologies. These questions highlight a diversity of topics that will establish soil protistology as a hub discipline connecting different fundamental and applied fields such as ecology, biogeography, evolution, plant-microbe interactions, agronomy, and conservation biology. We are convinced that soil protistology has the potential to be one of the most exciting frontiers in biology. - PublicationAccès librePatterns of earthworm communities and species traits in relation to the perturbation gradient of a restored floodplain
; ; ;Shrestha, Juna; Le Bayon Renée-ClaireLittle is known about the diversity and ecology of earthworms in floodplains, as well as their response to natural and anthropic perturbations (e.g. floods, river channelisation, floodplain restoration). We characterised the patterns of earthworm communities and species traits in the different habitats of a lowland restored floodplain in Switzerland. In addition to classical species-based metrics, such as species richness and Shannon diversity, species traits were used to calculate the community weighted means (CWMs) of traits and functional dispersion (FDis). We hypothesised that trait-based metrics would reveal clearer patterns than classical approaches. The distribution of earthworm traits varied among habitats in relation to changes in flooding frequency: poorly developed gravel bar soils most exposed to flooding were characterised by high abundance of small epigeic species and low abundance of large anecic species. Differences in anecic and endogeic earthworm community structure matched flood frequency. In agreement with our hypothesis, CWMs were more strongly correlated to environmental variables than species composition, diversity, or functional diversity. Based on these results, the ratio of the relative abundances of epigeic and anecic species, and the differences in species composition within anecic and endogeic ecological types of earthworms were identified as indicators of soil development in floodplains.